The term “steganography” generally means data hiding. One form of data hiding is digital watermarking. Digital watermarking is a process for modifying media content to embed a machine-readable (or machine-detectable) signal or code into the media content. For the purposes of this application, the data may be modified such that the embedded code or signal is imperceptible or nearly imperceptible to a user, yet may be detected through an automated detection process. Most commonly, digital watermarking is applied to media content such as images, audio signals, and video signals.
Digital watermarking systems may include two primary components: an embedding component that embeds a watermark in media content, and a reading component that detects and reads an embedded watermark. The embedding component (or “embedder” or “encoder”) may embed a watermark by altering data samples representing the media content in the spatial, temporal or some other domain (e.g., Fourier, Discrete Cosine or Wavelet transform domains). The reading component (or “reader” or “decoder”) analyzes target content to detect whether a watermark is present. In applications where the watermark encodes information (e.g., a message or payload), the reader may extract this information from a detected watermark.
A watermark embedding process may convert a message, signal or payload into a watermark signal. The embedding process then combines the watermark signal with media content and possibly another signals (e.g., an orientation pattern or synchronization signal) to create watermarked media content. The process of combining the watermark signal with the media content may be a linear or non-linear function. The watermark signal may be applied by modulating or altering signal samples in a spatial, temporal or some other transform domain.
A watermark encoder may analyze and selectively adjust media content to give it attributes that correspond to the desired message symbol or symbols to be encoded. There are many signal attributes that may encode a message symbol, such as a positive or negative polarity of signal samples or a set of samples, a given parity (odd or even), a given difference value or polarity of the difference between signal samples (e.g., a difference between selected spatial intensity values or transform coefficients), a given distance value between watermarks, a given phase or phase offset between different watermark components, a modulation of the phase of the host signal, a modulation of frequency coefficients of the host signal, a given frequency pattern, a given quantizer (e.g., in Quantization Index Modulation) etc.
The present assignee's work in steganography, data hiding and digital watermarking is reflected, e.g., in U.S. Pat. Nos. 6,947,571; 6,912,295; 6,891,959, 6,763,123; 6,718,046; 6,614,914; 6,590,996; 6,408,082; 6,122,403, 5,862,260, and US 2015-0156369 A1, application Ser. No. 14/725,399 (published as US 2016-0275639 A1), and in published specifications WO 9953428 and WO 0007356 (corresponding to U.S. Pat. Nos. 6,449,377 and 6,345,104). Each of these patent documents is hereby incorporated by reference herein in its entirety. Of course, a great many other approaches are familiar to those skilled in the art. The artisan is presumed to be familiar with a full range of literature concerning steganography, data hiding and digital watermarking.
One aspect of the disclosure is an apparatus comprising: a first LED providing illumination in the red spectrum; a second LED providing illumination in the blue spectrum; a third LED providing illumination in the green spectrum; a first 2D monochrome image sensor; a controller module for controlling illumination from the first LED, the second LED and the third LED; a watermark detection module for analyzing imagery captured by the first 2D monochrome image sensor. The imagery comprises a first image capture corresponding to illumination by the first LED and the second LED, minus a second image capture corresponding the illumination by the third LED. The first image capture comprises data representing a cyan channel and yellow channel, with each of the cyan channel and the yellow channel comprising a digital watermark embedded therein at a first signal polarity. The second image capture comprises data representing a magenta channel, the magenta channel comprising a digital watermark embedded therein at a second signal polarity that is inversely related to the first signal polarity.
Another aspect of the disclosure is an apparatus comprising: a first LED providing illumination in the red spectrum; a second LED providing illumination in the blue spectrum; a third LED providing illumination in the green spectrum; a first 2D monochrome image sensor; a second 2D monochrome image sensor; a controller module for controlling illumination from the first LED, the second LED and the third LED, in which the controller controls illumination from the first LED and the second LED at a time t, and then controls illumination from the third LED at a time t+x, where x is a time measured in milliseconds; and a watermark detection module. The watermark detection module analyzes imagery captured by the first 2D monochrome image sensor, in which the imagery comprises a first image capture corresponding to illumination by the first LED and the second LED, minus a second image capture captured by the second 2D monochrome image sensor. The second image captured corresponds to the illumination by the third LED, in which the first image capture comprises data representing a cyan channel and yellow channel, with each of the cyan channel and the yellow channel comprising a digital watermark embedded therein at a first signal polarity. The second image capture comprises data representing a magenta channel, the magenta channel comprising a digital watermark embedded therein at a second signal polarity that is inversely related to the first signal polarity.
Yet another aspect of the disclosure also relates to an apparatus comprising: an image sensor comprising rows and columns of photo-sensors; a first set of green filters overlaying a first set of photo-sensors; and a first set of magenta filters overlaying a second set of photo-sensors. The apparatus also comprises a digital watermark detector module configured to detect a digital watermark from a grayscale image comprising image data captured by the first set of magenta filters minus image data captured by the first set of green filters.
Further combinations, aspects, features and advantages will become even more apparent with reference to the following detailed description and accompanying drawing.